Joint Base Lewis-McChord is among the military installations that could be tapped temporarily to house some of the thousands of young Central American immigrants who have been detained at the U.S.-Mexico border, congressional sources said Monday.

Negotiations are still under way to place the minors in vacant housing at the South Sound base, said Kati Rutherford, spokeswoman for Rep. Denny Heck, D-Olympia.

Gov. Jay Inslee’s office also has been in touch with the Defense Department and the U.S. Department of Health and Human Services on the proposal, a spokeswoman said.

“This is an urgent humanitarian situation, and though this is a federal response, we are monitoring the situation carefully,” said Jaime Smith, Inslee’s spokeswoman.

About 25,000 unaccompanied minors crossed the U.S.-Mexico border in 2013 and about 60,000 are expected this year, overwhelming federal Health and Human Services facilities at the border, according to the agency.

So far, three military installations are helping house the children: Naval Base Ventura County in California, Fort Sill in Oklahoma and Joint Base San Antonio-Lackland in Texas. Officials have tried to make the quarters seem less institutional with touches such as bright blankets and bedspreads.

JBLM has some vacant housing in the form of World War II-era barracks that had been used in an annual ROTC exercise that was moved to Kentucky this year.

Defense Department personnel are not responsible for looking after the boys and girls at the installations where they are housed, according to press reports. The Department of Health and Human Services provides the security, food and medical needs of its young detainees on the military bases.

A Health and Human Services spokesman based in Washington, D.C., could not be reached for comment by deadline.

JBLM officials declined to comment on the negotiations.

Arizona Republican U.S. Sen. John McCain first disclosed the plan to move detained minors to Washington state in remarks Friday following a tour of a border patrol station in Nogales, Ariz.

He and other Republicans fault the Obama administration for sending a mixed message on immigration that McCain said encouraged Central American families to send their children north, according to press reports. He advocated more efforts to strengthen border security.

“Parents are sending their children thousands of miles, often times alone, to exploit a loophole in our immigration system,” McCain said, according to Tucson’s ABC 15. “They know if their children cross the border without them that they will be reunited with family in the United States.”

Officials in the Obama administration trace the influx of unaccompanied children at the border to drug-related violence in El Salvador, Guatemala and Honduras.